in a truly integrated bitcoin economy i don't think anyone will feel a 51% attack because in a truly integrated bitcoin economy most of the activity happens on other layers and the 51% attack can potentially be waited out. And if its a serious one military actions can be considered. I kinda like the idea of a relatively small task force that can go anywhere in the world within 24 hours and take a malicious mining operation out of service if it insists on being malicious.